Traditionally, a type of electrical junction box which has a unit storing room that accommodates an electronic control unit including electrical control components is proposed (refer to a patent document 1). The electrical junction box has a storing room which accommodates a plurality of electric wires (harness) and connectors which are connected to the electronic control unit, besides the unit storing room which accommodates the electronic control unit. The electrical junction box packs up these components compactly and is installed in a vehicle indoor room. When the electronic control unit is to be accommodated in the unit storing room, the electrical junction box in which the electric wires, connectors and the like are arranged in advance is prepared by the electrical manufacturer or the electric wire arranging dealer, and then, the electronic control unit is accommodated in the unit storing room of the electrical junction box by the automobile manufacturer.